The microwave treatment of cancer is a growing clinical alternative to X-ray treatment and chemotherapy. Basically, the microwaves heat the tissue. Malignant tumors have been found to be often more sensitive to heat than normal tissues, so the careful application of microwaves can destroy the malignant tumors while the normal tissue survives.
In Kantor U.S. Pat. No. 4,108,147, a microwave applicator is disclosed. It comprises an open-bottom container having a pair of opposed Teflon slabs spaced from each other. The microwaves are propagated in the space between the slabs for treatment of skin exposed to the open bottom of the applicator.
Various disadvantages of this design of applicator exist. First, the applicator is designed for use with diathermy radiation of about 2.45 GHz. A disadvantage of this is that such radiation only penetrates a relatively small distance into the tissue, typically less than 2 cm. Furthermore, superficial burns on the skin are a continuous problem with a structure like this, since the microwave absorption is concentrated near the skin surface.
Also, microwave applicators have been utilized at 915 MHz among other frequencies, but with apparent effective penetration of only 1 or 2 cm. into the muscle because of the inherent lack of penetration capability of microwaves at that frequency (Lehmann et al: Evaluation of a Therapeutic Direct-Contact 915-MHz Microwave Applicator for Effective Deep-Tissue Heating in Humans. IIEE Trans Microwave Theory Tech; 26(8): 556-563 (1978)).
In accordance with this invention, a microwave applicator is provided for irradiating the skin surface of a patient, but with substantially increased effective penetration of 5 to 6 cm. At the same time, the danger of skin burns can be greatly reduced with the method and apparatus of this invention, with the apparatus being inexpensive and compact for ease of clinical use.